Layered potassium cobaltate K0.36CoO2 has been successfully synthesized from KOH fluxes at 480 degrees C. The K0.36CoO2 sample can be oxidized and intercalated with water by treatment in KMnO4 and K2S2O8 solutions. K0.12CoO2 center dot 0.8H(2)O and K0.16CoO2 center dot 0.6H(2)O have been obtained after the KMnO4 and K2S2O8 treatment, respectively. The diffraction peaks of K0.12CoO2 center dot 0.8H(2)O and K0.16CoO2 center dot 0.6H(2)O can be well indexed by a hexagonal cell similar to the monolayer hydrate NaxCoO2 center dot yH(2)O. Afterdehydration, the major phases have an orthorhombic structure similar to Na0.5CoO2 and show semiconductor behavior. Both K0.12CoO2 center dot 0.8H(2)O and K0.16CoO2 center dot 0.6H(2)O are primarily paramagnetic and show metallic behavior. K0.16CoO2 center dot 0.6H(2)O has a spin-glass-like transition or other magnetic fluctuations around 56 K. The spin-glass-like transition or the regions of magnetic phase separation are reduced in K0.12CoO2 center dot 0.8H(2)O due to the increasing of the intercalated water. We also discussed similarities and differences between the structural and physical properties of KxCoO2 and NaxCoO2.
Reversible protein phosphorylation networks play essential roles in most cellular processes. While over 500 kinases catalyze protein phosphorylation, only two enzymes, PP1 and PP2A, are responsible for more than 90% of all serine/threonine phosphatase activity. Phosphatases, unlike kinases, achieve substrate specificity through complex subunit assembly and post-translational modifications rather than number. Mutations in several of the PP2A subunits have been identified in human cancers, suggesting that PP2A may act as a tumor suppressor. Adding further complexity, several residues of the catalytic subunit of PP2A can be reversibly phosphorylated, and the C-terminal leucine residue can be reversibly methylated. Protein phosphatase methylesterase-1 (PME-1) is specifically responsible for demethylation of the carboxyl terminus. Methylesterification is thought to control the binding of different subunits to PP2A, but little is known about physiological significance of this post-translational modification in vivo. Recently, PME-1 has been identified as a protector of sustained ERK pathway activity in malignant gliomas. PME-1 knockout mice generated by targeted gene disruption result in perinatal lethality, underscoring the importance of PME-1 but hindering biological studies. The Scripps Research Institute Molecular Screening Center (SRIMSC), part of the Molecular Libraries Probe Production Centers Network (MLPCN), identified a potent and selective PME-1 inhibitor probe, ML174, by high-throughput screening using fluorescence polarization-activity-based protein profiling (FluoPol-ABPP). ML174, with an IC50 of 10 nM, is based on the aza-beta-lactam scaffold and is selective for PME-1 among serine hydrolases in human cell line proteomes as assessed by gel-based competitive-activity-based protein profiling. Among more than 30 serine hydrolase anti-targets, ML174 is selective at 1 μM. Additionally, ML174 was shown in situ to be highly active against PME-1 and to result in 85% reduction of demethylated PP2A. We previously reported a modestly potent 500 nM inhibitor that was selective for PME-1, the first reported selective PME-1 inhibitor. ML174 is 50 times more potent and from an entirely different structural and mechanistic class of inhibitors. Due to its much higher potency, ML174 has greater potential for use in long time-course in situ studies, and is a much better candidate for in vivo applications.
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